The invention relates to the general field of turbine engine compressors, in particular for an airplane turboprop or turbojet. More precisely, the invention relates to a device enabling variable pitch diffuser vanes of a compressor stage to be guided.
The high pressure compressor of an aviation turbine engine has a plurality of diffuser stages with variable pitch vanes that alternate with stages of rotor blades. The diffuser vanes serve to modify the flow characteristics of the gas depending on the operating speeds of the turbine engine.
Each variable pitch diffuser vane has a control pivot at its head and a guide pivot at its foot, the control pivot passing through a stator jacket (known as the casing) of the turbine engine and co-operating with a control member for varying the pitch of the vanes, while the guide pivot is pivotally mounted in a bushing received in a socket in an inner ring of the turbine engine. By acting on the control member, it is thus possible to vary the pitch of the vanes in the stage in question.
The compressor casing is generally made as two half-shells in order to facilitate assembly. However, in order to reduce weight and increase the performance of the assembly, proposals have been made to make the casing as a single piece (extending over 360°). Unfortunately, when the compressor casing is a single piece in the tangential direction, it is found to be considerably more complicated to install the various portions of the compressor inside it. In particular, having recourse to a casing made of two half-shells enables the stator elements of the compressor to be assembled individually and then to be put in place around the elements of the rotor. With a single-piece casing, it is necessary to assemble in alternation a rotor stage and then a stator stage.
Furthermore, in order to dimension the rotor line of the compressor, its shroud line needs to be as close as possible to the flow passage for the stream of gas passing therethrough. This has the consequence of reducing the space available under the passage, and thus of making it necessary to reduce the radial size of the device for guiding the diffuser vanes.
Document FR 2 875 270 describes a diffuser vane guide device in which the inner ring under the vanes is made up of two half-rings clamped together by axial keys, a sealing member support being mounted on the inner ring. With such a device, the spacing between the vane guide pivots must be sufficient to enable the keys to be received therein without giving rise to cracks. Furthermore, that device presents relatively large radial size.